Various machines have been developed to separate particles of high density such as gold, iron or tin from tailings and other slurry streams using centrifugal concentration, using the centrifugal force created in a rotating bowl to separate the high density particles from the lower density slurry. The present applicant for example has invented batch centrifugal concentrators which are the subject of U.S. Pat. No. 4,824,431 and Canadian Patent no. 2149978, which are incorporated herein by reference. Such machines are designed to maximize the throughput of slurry, and are designed to withstand the heavy duty and wear arising from a relatively long-term operation at a mine. The rotating bowl is typically mounted on a shaft supported on large bearings, and is rotated by a motor beneath the machine which drives a drive belt connected to a sheave on the rotor shaft.
Artisanal or small-scale mining is a mining activity which involves people working with simple tools and equipment, outside the legal and regulatory framework. Currently, it is estimated that there are many millions of people involved in artisanal mining around the world and that number is growing with the elevated price of gold. It takes place in the remote parts of the world's poorest countries. It usually involves the activities of single individuals or a small group of individuals who are impoverished and exploiting marginal deposits in harsh conditions. One common form of artisanal mining is placer gold mining or panning for gold. In order to separate the retrieved gold from the ore, the artisanal miner will often crush the ore and use mercury which combines with the gold to form an amalgam, and which can be separated from the other material as “cake”. The miners then heat the cake to burn off the mercury, leaving a residue of gold as well as causing health and environmental problems. There is therefore a need for a simple and inexpensive but environmentally safe method for artisanal miners to separate gold from particulate material.